As a transmission ratio control for a continuously-variable transmission, a control mode (hereinafter referred to as “normal mode”), which basically controls the transmission ratio on a variable basis in accordance with the operation condition, and which, when the driver's demand for acceleration is strong, makes a transition to a control mode (hereinafter referred to as “linear mode”) to provide the transmission ratio such that the input revolution speed of the continuously-variable transmission becomes high compared to the normal mode at the same vehicle speed. That is, the linear mode is a mode to moderate the change of the transmission ratio compared to the normal mode.
For example, in JP2002-372143A, when the accelerator opening exceeds a threshold, it is determined that the demand for acceleration is strong, and a transition to the linear mode to moderate the change of the transmission ratio is made. By this means, when the engine revolution speed increases due to the increase of the throttle opening, the driving force also increases quickly. In other words, the delay in time after the throttle opening increases until a feeling of acceleration is gained becomes short, so that it is possible to alleviate the disagreeable feeling to be given to the driver.
Then, when the accelerator opening decreases by a predetermined amount during linear mode drive, it is determined that the demand for acceleration has lowered, and the linear mode is cancelled and a transition to the normal mode is made.